The whisky compass (i.e. magnetic) is slightly wrong most of the time, by a predictable (but varying) amount - but it is cheap, light, simple, requires no power, and has worked for 1,000 years (except around the Poles).
The basic deal is that aviation is a "system" - controllers, charts, plates, runway headings, radio beacons, etc, etc. That has to work, universally, for any type of airplane.
From a Piper Cub with just a whisky compass, to a Cessna with a gyroscopic compass (that drifts, and therefore needs a whisky compass for periodic correction), to airliners with IRU's or GPS units - that may happily work with no magnetic reference at all (unless something goes wrong and needs cross-checking).
Busy controllers (as just one example) can't be handling TWO systems - giving 747s True vectors, and the little guys Magnetic vectors.
So the system can't abandon magnetic North just yet, even though many specific planes can (or already do, effectively). And as aterpster says, that will be the ideal (except for the gals/guys in Piper Cubs).
As others have said - there are remote spots in the Polar regions, where magnetic doesn't work - Magnetic "North" may be W, E or even S of your position, in grid and True terms.
The commercial systems can adapt (mostly) - and the little guys pull out the charts and pencil and do some math (or these days, may have an "app") and correct for the error that way.